The present invention generally relates to a unique electric over air (EOA) shift system for a vehicle transmission assembly. More particularly, this invention provides a single non-continuos duty solenoid valve which reduces packaging requirements within the vehicle.
Heavy-duty vehicle transmissions typically provide the ability to engage a large number of gear ratios for driving the vehicle. Usually, main transmission gearbox house a number of gears that are selectively engaged to achieve a particular gear ratio for optimal vehicle performance. An auxiliary or range gearbox is often additionally provided to increase the number of available gear ratios. The range gearbox typically includes one or more range gears that are selectively engaged by an pneumatic system to operate the transmission in one of several ranges. Usually the range gearbox includes a low range and a high range. For example, the low range is typically associated with the lower gears in the transmission such as first through fifth gear. When the range gear box is switched into the high range, the same gears in the transmission main gear box that were used for first through fifth gear are now used for sixth through tenth gear.
Range gearbox assemblies are typically attached to a transmission main gearbox housing. A shaft from the main gearbox is coupled to a shaft for the range gearbox. One recent development is the use of electric controls for air cylinders to power the range function. These so-called electric over air gearbox configurations include a range gearbox housing containing the range gears, a range piston housing containing the range actuation piston, two solenoids, an air supply, and a range selection switch.
The solenoids allow selective communication of air from the air supply to either side of the range piston. By actuating the range piston the high range or low range gears are selected. The solenoids are continuous duty solenoids. In other words, the solenoid valve is always energized to either an open or a closed position.
After the operator has shifted through the low gear range, the range selection switch may be activated. When the switch is activated a first solenoid is opened to atmosphere and the second solenoid communicates air from the air supply to the range piston. The piston thereby shifts the range gearbox into the high gear range so that the same gears in the transmission main gearbox that were used for low range are now used for the high range. Similarly, to shift into the low gear range the second solenoid is opened to atmosphere and the first solenoid communicates air from the air supply to the range piston. The piston thereby shifts the range gearbox into the low gear range.
This range system configuration requires space for two solenoids. There is limited space available in the vehicle. Mounting the two solenoids so that they are located between the air regulator and the range piston housing takes up valuable space. Also, because the solenoids are continuous duty they must be constantly supplied with electricity. This requires a large magnetic coil which requires additional space and must typically be provided in an open location to receive an airflow for cooling. This type of gearbox configuration therefore has multiple packaging restrictions.
Thus, it is desirable to minimize the number of solenoid valves to provide a range system that is compact, reduces cost, and which provides for packaging advantages within the vehicle. Further, it would also be desirable to eliminate the requirement for continuous duty solenoids to reduce the constant stress on the solenoids. Maintenance requirements would thereby be reduced and the life of the range system would be increased.
A present invention provides a transmission having a unique EOA actuation system for an auxiliary transmission system such as a range system. A range system generally includes a range gearbox and a range piston housing which contains a range gearbox actuator. To shift the range gearbox a range switch on the transmission shift lever allows the vehicle driver to actuate a desired range shift. When the range gearbox is switched into a high range, for example, the same gears in the transmission main gear box that were used for first through fifth gear are now used for sixth through tenth gear.
In a preferred embodiment, the range gearbox is shifted by an EOA system that includes an air supply, a controller and a single solenoid. The solenoid is preferably a spring centered, 4-way solenoid. Because the solenoid is spring centered, its unenergized state is a neutral condition which maintains the actuator at its current position within the range piston housing without the necessity of maintaining the energization of the solenoid.
The solenoid is selectively operated by the controller. If the solenoid is provided with a voltage, the solenoid allows the communication of air to a first side of the range piston housing. If the voltage is reversed, air is directed to a second side of the range piston housing. The actuator is thereby accordingly shifted by the air pressure to shift the range gears.
The controller also includes a timer function. When the driver actuates the range switch, the solenoid valve is energized. The controller operates the appropriate valves to open the appropriate ports. The actuator is forced under air pressure to shift the range gearbox into the high or low range. Because the actuator does not reach its full travel immediately the controller maintains the solenoid in an energized condition for a predetermined period of time until the shift has been accomplished. Upon completion of the shift, the controller deenergizes the solenoid which then returns to its neutral condition.
The configuration of the present invention provides significantly improved packaging which increases available space for other components. The controller also allows a single non-continuos duty solenoid to replace the pair of continuous duty solenoids in known systems. The non-continuos duty solenoid also reduces maintenance requirements while increasing the EOA system life.